The present invention relates generally to a means for and method of illuminating a given area of known configuration from a source of light which is located at a point spaced from the area to be illuminated, and more particularly to a means for and method of illuminating the lasing zone in the dye chamber of a master dye laser oscillator with light from a pumping beam.
A typical dye laser oscillator includes, among other components, a dye cell, a beam expander, an etalon, a grating assembly, and an output coupler which supports an end mirror. A pump laser beam, for example copper vapor laser beam, is directed into a particular zone within the dye cell which is designed to receive a continuous supply of dye therethrough. This causes the dye to lase in the zone being illuminated by the pump beam and thereby produce a dye beam which is directed through the beam expander, the latter serving to expand the beam in one direction, whereby to produce a ribbon of light. This ribbon passes through the etalon and onto the grating which directs the beam (actually a portion thereof) back through the etalon, the beam expander and into the dye cell where it is amplified before finally impinging on the end mirror of the output coupler. A portion of this beam passes through the end mirror and forms the output dye beam for the overall oscillator. The rest of the beam is reflected back into and through the dye cell where the process is repeated for purposes of amplification. The etalon and grating assembly serve to limit the ultimately produced beam to a particular narrow wavelength band, the grating serving as a coarse tuning mechanism while the etalon serves as a fine tuning mechanism.
In the dye laser oscillator of the general type just described, it is important that all of the components just mentioned be precisely optically aligned relative to one another. One step which is taken to insure that this is the case is to use the intended lasing zone within the dye cell (e.g., the zone which is supposed to be illuminated by the pump laser beam) as a frame of reference for aligning purposes. Thus, it is essential that the entire lasing zone to be illuminated is, in fact, illuminated by the pump laser. At the same time, it is inefficient and quite costly from an economic standpoint to illuminate an area even slightly larger than the intended lasing zone since the cost of producing pump beam photons is relatively higher. Moreover, since the lasing zone itself is quite small, any spillage beyond the zone can be quite significant.
Heretofore, one way of illuminating the lasing zone in the dye cell of a dye laser oscillator with a pumping beam has been by means of optical concentration utilizing a single glass lens. While this approach may or may not be satisfactory if the cross section of the pumping beam is relatively large, the present invention contemplates a relatively small pump beam cross section in combination with a lasing zone which is relatively large in the lengthwise direction and relatively small widthwise. Specifically, the present invention contemplates producing a relatively large number of low power, secondary pump beams which are combined by means of multiplexing to produce a single output beam for pumping the dye passing through the dye cell. However, for such an output beam to be usable, it must be purified, that is, act as a single, homogeneous beam of light without any traces of the prior multiplexing of the lower power secondary beams. As will be seen hereinafter, the ultimately produced output beam is purified by passing it through a sufficiently long optical fiber. At the same time, using an optical fiber as a means of conveying a pumping beam to the dye cell of the dye laser oscillator has other advantages. However, considering the cross section of the optical fiber contemplated which is on the order of 0.6 mm in diameter and the size of the lasing zone contemplated, specifically 8.00 mm long by 0.25 mm wide, it is extremely difficult to accurately and reliably direct all of the light from such a fiber uniformly into such a zone, especially by means of optical concentration.